Power Factor Correction (PFC) circuit is widely used in power converter in order to control phase of input current and improve power factor. FIG. 1 illustrates a waveform diagram in a PFC control. An input voltage Vin is a half-sine waveform signal, and is usually rectified from a power grid which is an Alternating-Current (AC) sine wave. Waveform shape of an input current Iin needs to follow waveform shape of input voltage Vin to implement PFC control, that is phase of input current Iin should be same with phase of input voltage Vin. Generally, a relatively high input voltage Vin corresponds to a relatively low average input current Iin_avg. In a switching mode PFC circuit, waveform shape of input current Iin is a saw tooth shape, and power factor can be improved by controlling waveform shape of average input current Iin_avg to follow waveform shape of input voltage Vin, as a result PFC control is achieved.
At the meantime, the international energy agency puts forward high requirements in power conversion efficiency of PFC circuit. However, light load efficiency of the present PFC products is hard to meet the requirements well.
Accordingly, an improved PFC circuit with high efficiency, especially at light load is required.